Implement an optionalBool, to be used as a cli.GenericFlag

This mirrors the behavior of cli.BoolFlag, but records and explicit
"present" indication.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

cmd/skopeo/flag.go

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"strconv"
+
+	"github.com/urfave/cli"
+)
+
+// optionalBool is a boolean with a separate presence flag.
+type optionalBool struct {
+	present bool
+	value   bool
+}
+
+// optionalBool is a cli.Generic == flag.Value implementation equivalent to
+// the one underlying flag.Bool, except that it records whether the flag has been set.
+// This is distinct from optionalBool to (pretend to) force callers to use
+// newOptionalBool
+type optionalBoolValue optionalBool
+
+func newOptionalBoolValue(p *optionalBool) cli.Generic {
+	p.present = false
+	return (*optionalBoolValue)(p)
+}
+
+func (ob *optionalBoolValue) Set(s string) error {
+	v, err := strconv.ParseBool(s)
+	if err != nil {
+		return err
+	}
+	ob.value = v
+	ob.present = true
+	return nil
+}
+
+func (ob *optionalBoolValue) String() string {
+	if !ob.present {
+		return "" // This is, sadly, not round-trip safe: --flag is interpreted as --flag=true
+	}
+	return strconv.FormatBool(ob.value)
+}
+
+func (ob *optionalBoolValue) IsBoolFlag() bool {
+	return true
+}

cmd/skopeo/flag_test.go

@@ -0,0 +1,137 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/urfave/cli"
+)
+
+func TestOptionalBoolSet(t *testing.T) {
+	for _, c := range []struct {
+		input    string
+		accepted bool
+		value    bool
+	}{
+		// Valid inputs documented for strconv.ParseBool == flag.BoolVar
+		{"1", true, true},
+		{"t", true, true},
+		{"T", true, true},
+		{"TRUE", true, true},
+		{"true", true, true},
+		{"True", true, true},
+		{"0", true, false},
+		{"f", true, false},
+		{"F", true, false},
+		{"FALSE", true, false},
+		{"false", true, false},
+		{"False", true, false},
+		// A few invalid inputs
+		{"", false, false},
+		{"yes", false, false},
+		{"no", false, false},
+		{"2", false, false},
+	} {
+		var ob optionalBool
+		v := newOptionalBoolValue(&ob)
+		require.False(t, ob.present)
+		err := v.Set(c.input)
+		if c.accepted {
+			assert.NoError(t, err, c.input)
+			assert.Equal(t, c.value, ob.value)
+		} else {
+			assert.Error(t, err, c.input)
+			assert.False(t, ob.present) // Just to be extra paranoid.
+		}
+	}
+
+	// Nothing actually explicitly says that .Set() is never called when the flag is not present on the command line;
+	// so, check that it is not being called, at least in the straightforward case (it's not possible to test that it
+	// is not called in any possible situation).
+	var globalOB, commandOB optionalBool
+	actionRun := false
+	app := cli.NewApp()
+	app.EnableBashCompletion = true
+	app.Flags = []cli.Flag{
+		cli.GenericFlag{
+			Name:  "global-OB",
+			Value: newOptionalBoolValue(&globalOB),
+		},
+	}
+	app.Commands = []cli.Command{{
+		Name: "cmd",
+		Flags: []cli.Flag{
+			cli.GenericFlag{
+				Name:  "command-OB",
+				Value: newOptionalBoolValue(&commandOB),
+			},
+		},
+		Action: func(*cli.Context) error {
+			assert.False(t, globalOB.present)
+			assert.False(t, commandOB.present)
+			actionRun = true
+			return nil
+		},
+	}}
+	err := app.Run([]string{"app", "cmd"})
+	require.NoError(t, err)
+	assert.True(t, actionRun)
+}
+
+func TestOptionalBoolString(t *testing.T) {
+	for _, c := range []struct {
+		input    optionalBool
+		expected string
+	}{
+		{optionalBool{present: true, value: true}, "true"},
+		{optionalBool{present: true, value: false}, "false"},
+		{optionalBool{present: false, value: true}, ""},
+		{optionalBool{present: false, value: false}, ""},
+	} {
+		var ob optionalBool
+		v := newOptionalBoolValue(&ob)
+		ob = c.input
+		res := v.String()
+		assert.Equal(t, c.expected, res)
+	}
+}
+
+func TestOptionalBoolIsBoolFlag(t *testing.T) {
+	// IsBoolFlag means that the argument value must either be part of the same argument, with =;
+	// if there is no =, the value is set to true.
+	// This differs form other flags, where the argument is required and may be either separated with = or supplied in the next argument.
+	for _, c := range []struct {
+		input        []string
+		expectedOB   optionalBool
+		expectedArgs []string
+	}{
+		{[]string{"1", "2"}, optionalBool{present: false}, []string{"1", "2"}},                                       // Flag not present
+		{[]string{"--OB=true", "1", "2"}, optionalBool{present: true, value: true}, []string{"1", "2"}},              // --OB=true
+		{[]string{"--OB=false", "1", "2"}, optionalBool{present: true, value: false}, []string{"1", "2"}},            // --OB=false
+		{[]string{"--OB", "true", "1", "2"}, optionalBool{present: true, value: true}, []string{"true", "1", "2"}},   // --OB true
+		{[]string{"--OB", "false", "1", "2"}, optionalBool{present: true, value: true}, []string{"false", "1", "2"}}, // --OB false
+	} {
+		var ob optionalBool
+		actionRun := false
+		app := cli.NewApp()
+		app.Commands = []cli.Command{{
+			Name: "cmd",
+			Flags: []cli.Flag{
+				cli.GenericFlag{
+					Name:  "OB",
+					Value: newOptionalBoolValue(&ob),
+				},
+			},
+			Action: func(ctx *cli.Context) error {
+				assert.Equal(t, c.expectedOB, ob)
+				assert.Equal(t, c.expectedArgs, ([]string)(ctx.Args()))
+				actionRun = true
+				return nil
+			},
+		}}
+		err := app.Run(append([]string{"app", "cmd"}, c.input...))
+		require.NoError(t, err)
+		assert.True(t, actionRun)
+	}
+}